Printing cut



PRINTING 'GUT Filed Oct. 28, 1935 IN VENTOR.

Josqa L7 @C iz'arz/ BY .wdzflmm ATTORNEY.

Federated? en. 34,, i3?

UNHE

This inventionrelates in general to improvements in the photoengravingprocess of producing a printing plate or cut and has more particularreference to the building up the relief in a cut of this kind, to getrid of the unexposed gelatin in a photographic plate and therebypreventing a blurring of the shadows, and in providing a relief platemounted upon a. resilient backing which is adapted to produce a printingcut in U which the printing make-ready is obviated. In

producing an inexpensive photographic printing plate of this type, aphotographic negative is made from which a photographic copy or positiveis produced with the surface broken up into dots, 15 surfaces or lines.This positive is then chemically treated to form a relief plate in whichthe dots or lines stand out in relief while the other portions of theplate are etched below the printing surface.

so When this process is applied to a positive film having acelluloidbacking with a sensitized gelatin emulsion, the exposedpositive film is treated in a warm bath which washes away the gelatinemulsion between the surfaces or dots which have been exposed and whichform the printing surface. As the high-light dots swell considerablymore than the shadow dots, a plate of this kind ordinarily makes a poorplate for printing due to the uneven printing surface which ispresented.

L) By treating the high-light dots with 'a suitable solution containinglead nitrate or other photographic chemcials, the printing dots arebuilt up to give a greater relief to the printing surface but theunevenness of the high-light and shadow dots makes the entire platesurface so-uneven that it does not provide a satisfactory printingsurface.

The present invention therefore relates to the preparation of aphotographic plate of this kind which is then applied to and mountedupon a backing block or even upon a curved printing plate by means of ayielding cushion or blanket preferably of rubber or a similar yieldingmaterial in which is combined the softness of the backing with the hardtreated printing surface of the film so that in the actual operation ofprinting the high-light dots are squeezed down into the rubber backingwithout distortion or the printing surface is leveled off by theresilient mounting 50 so that a plate of this kind will print almostequally well upon a smooth paper or upon a very rough or coarse texturedpaper without requiring extra deep etching in the plate, withoutrequiring an extra heavy pressure upon the out which tends toobjectionably emboss the paper, and thus also providing an automaticmake-ready plate applicable to any ordinary class of paper.

Another feature of this invention is that rubber and rubber solutionsare affected-to considerable extent by printing ,inks, chemicals andcleaning solutions containing benzine, but by mounting the film on topof "a rubber blanket or cushion the rubber is protected by the filmexcept at the edge, and a coating of shellac or other pervious materialmay be added about the exposed edge of the cushion which will furtherprotect the exposed edges from any action which tends to loosen thecontact of the rubber cushion with the printing block or the film, or todeteriorate the rubber about the edges thereof. It is also apparent thatthis same process or a suitable modification of it may be applied to athin metal sheet which is suitably etched by photographic or otherprocesses and mounted on a block with a rubber backing. Or a sensitizedsolution or film may be applied to a thin coating of metal, bakelite,linoleum, or the like, and backed with a resilient cushion for producinga printing out which will operate in a similar manner. The photographicfilm and its rubber backing may also be applied equally well to a curvedbacking plate used in rotary printing presses.

Other objects of the invention will appear in the specification, theaccompanying drawing illustrating somewhat diagrammatically the processof producing and the construction of the cuts, in which,

Figure 1 represents a sectional view of an ordinary positive film withhigh and low printing dots and the gelatin washed out between them;

Fig. 2 represents a sectional view of a portion of such a film treatedwith a solution which builds up the printing dots and with an appliedresilient backing;

Fig. 3 represents a sectional view of a printing plate of this. kindwhen subjected to printing pressure which distorts the resilient backingto bring all of the dots approximately into the same printing plane; and

Fig. 4 shows a section of a printing cut to celluloid backing 8 has anumber of high-light dots 9 which are produced in a well known manner byexposing a plate of this kind coated with gelatinous film impregnatedwith silver salts or silver bromide, exposed photographically, developedand fixed, then put into a hardening bath 55 the rubber itself.

which hardens only the silver sensitized by light, and the gelatinoussubstance between the highlight dots is then washed out in a bath ofwarm water, leaving the high-light dots extending to a greater or lessdegree above the surface of the backing 8 and above the shadow dots orshadow surface. If the gelatinous substance between the high-light andshadow dots is not well washed out, it tends to blur the shadows and tomake a smear or dull surface which is not well defined and distinct inappearance.

The plate may therefore be further treated in a solution to build up thehigh-light dots more than the shadow dots and to render them both moreclearly distinct even though the height of the dots and their differencein elevation from the backing plate 8 may be somewhat accentuated. Asuitable bath for this purpose consists of lead nitrate, 1 ounce;potassium ferrocyanide, 1 ounces; water, 24 ounces; glacial acetic acid,1

ounce. v

By treating the positive plate in this bath, the unevenness of theprinting dots is increased or accentuated so that the actual printingsurface may be more uneven as represented in Fig. 2, with the additionof the lead nitrate, than in the normal appearance of the plate as shownin Fig. 1, so that this plate would not make an equallypleasingimpression upon different kinds of paper without considerable work onthe variation of the cut known as the printing make-ready.

Instead of treating the exposed positive plate first with a hardeningbath and, then with the lead nitrate solution as above set forth, anexposed plate may be treated with a solution of vanadium or uraniumchloride after developing and fixing the image which acts upon thesensitized silver salts, hardening and building them up at the top andalso loosening the unexposed gelatin surfaces or dots so that when putin hot water of approximately 120 the unexposed gelatin comes out veryreadily, leaving the high-light and shadow dots at various heights asrepresented in Fig. 2, cleaning out the shadows to the celluloid baseand thereby producing a good clear dot which makes a distinct printingsurface. A suitable solution for thus hardening and building up the dotsis; vanadium chloride, 16 grains; ferrocyanide, 16 grains; 1 dram ironchloride; dissolve the above in ounces of water, then make a saturatedsolution of oxalic acid and add two ounces of the saturated solution tothe above mixture.

Treatment of the positive film after the vanadium chloride. bath seemsto toughen the metal topped sensitized gelatin dots and when thepositive plate thus produced or as produced with the lead nitrate bathis suitably dried it is ready for application to a printing block.

, A resilient cushion II is applied to the back of the printing plateand to a printing block it or a suitable printing plate. At each side ofthe cushion II is a stiffening fabric layer l2 which prevents unduespreading of the rubber blanket and prevents the rubber from squeezingout between the plate and the block under high printing pressure.Preferably the fabric layers are vulcanized in place at the top andbottom surfaces where they provide better gluing attachment surfacesthan The top layer of non-resilient material also raises the printingplate high enough above the .rubber to prevent the rubber from squeezingout at the edge and forming a printing blur at' the edge of the plate.

When printing pressure is applied to a cut of ,this kind, the outer orprinting surfaces of the tized gelatin film,

dots are all brought into the same plane because of the resilience ofthe cushion I l which in efiect is distorted as represented in Fig. 3 tobring the printing dots 9 into alignment at the printing surface asrepresented by the line iii, the bases of the dots and the base of thecelluloid plate 8 being more or less distorted, depending upon theheights of the dots as compared with the other ones. Thus theapplication of therubber cushion to a film with a backing plate, as 8,combines the stiffness of. the plate and the softness of the cushion llto produce an even printing surface when printing pressure is applied tothe cut.

This combination of a resilient backing and photographicfilm as appliedto a printing block 14 usually of solid or laminated wood of such aheight that the printing surface is at the proper level for cuts of thistype. The resilient cushion II is attached to the upper surface of theblock and to the back of the film by any suitable cement which is foundto adhere more firmly to the vulcanized fabric 12 than to the rubberalone, and a protective coating or fillet of shellac or similar materialI5 is commonly applied about the exposed edges of the resilient coatingbelow the i printing plate in order to prevent the detrimental effect ofprinting ink or the cleaning material for such printing ink from accessto or contact with the resilient backing or by the cement by which thecushion is secured in place.

This invention therefore relates to the provision of a printing cut froma photographic plate in which the unevenness of the printing dots isaccentuated and the printing surfaces thereof built up by a metaldeposit, and then the unevenness is corrected by means of resilient backing which takes up the unevenness and provides a printing surface whichunder suitable pressure produces a high-class, clear-cut, distinctiveprint upon smooth or rough-textured paper without the necessity of extrawork for printers makeready and without requiring a high printingpressure or deeply etched plates which tend to distort and emboss arough-textured paper.

If desired, the sensitive emulsion may be apv plied directly to a rubberor other soft or flexible material thereby eliminating the attachment ofa film to a soft rubber layer and instead of being applied to a flatplate or block it is apparent that the emulsion upon such a rubberbacking may be applied to a curved printing plate as commonly used.

I claim:

1. The process of producing a photographic printing plate from a thinflexible positive film coated with a sensitized gelatine emulsion whichcomprises the photographic formation of relief printing surfaces ofhigh-light and shadow dots of varying heights on said film, inaccentuating the height variation of the dots, and in applying aresilient backing to the film which will permit the latter to yield forbringing the printing surfaces of the dots into alignment when printingpressure is applied to the backing. 2. The process of producing aphotographic printing plate which comprises producing a photographicpositive upon a thin flexible sensiin developing the image, in washingout the excess gelatin, in building up the high-light and shadowdotsforming the image and allowing them to dry and harden with their outersurfaces at various heights on the film, in

applying to the'back of the film a resilient material which will yieldwith the film to such an extent that the outer printing surfaces of thedots may be brought into alignment, and in mounting the resilientbacking and film upon a printing block for applying printing pressure tobring the printing surfaces-of the dots into alignment for printing. I

3. A relief printing plate comprising a thin flexible photographicpositive film having relief surfaces composed of high-light and shadowdots in which the high-light dots are higher than the shadow dots, andmeans for equalizing the height of the dots for printing so that thehigh-light dots will not be unduly squeezed under the printing pressure,said means comprising a printing block and a resilient backinginterposed between the thin flexible film and the block whereby saidresilient backing and film will yield under pressure to bring theprinting surfaces of the dots substantially into alignment.

4. A relief printing plate comprising a thin flexible photographicpositive film having relief surfaces composed of high-lights and shadowdots in which the high-light dots are higher than the shadow dots, andmeans for equalizing the height of the dots for printing so that thehighlight dots will not be unduly squeezed under printing pressure, saidmeans comprising a soft rubber backing, and a. layer of fabricinterposed between the rubber backing and film, in association with aprinting block, whereby the film, fabric, and rubber backing will yieldunder pressure to bring the printing surfaces of the dots substantiallyinto alignment and the layer of fabric will prevent undue spreading ofthe rubber dots will not be unduly squeezed under printing pressure,said means comprising a soft rubber backing, a layer of fabricinterposed between the backing and film, in association with a printingblock and a layer of fabric between the printing block and backing,whereby the film, backing, and

interposed fabric will yield under pressure to bring the printingsurfaces of the dots substantially into alignment and the layers offabric will prevent undue spreading of the soft rubber backing.

JOSEPH T. COCHRAN.

